Integrated circuits are found in a wide variety of equipment, including household appliances, consumer electronics, communications systems, automotive systems, aircraft, and the like. As dependence on integrated circuits has increased, the reliability of these devices has increasingly become an important concern. In general, as devices scale to smaller silicon fabrication technologies, they often become less reliable for the same use conditions.
There are many failure mechanisms that affect the reliability of an integrated circuit. Several of these mechanisms are influenced by the gate oxide thickness of the integrated circuit, for example, Bias Temperature Instability (BTI) and Time Dependent Dielectric Breakdown (TDDB). Bias Temperature Instability can be either negative or positive, and relates to the change in threshold voltage and drain current with a change in gate oxide thickness of a metal-oxide-semiconductor field-effect transistor (MOSFET) in an integrated circuit. Time Dependent Dielectric Breakdown is a failure mechanism in MOSFETs, when the gate oxide breaks down as a result of long-time application of relatively low electric field. The breakdown is caused by formation of a conducting path through the gate oxide to the substrate due to electron tunneling current, when MOSFETs are operated close to or beyond their specified operating voltages. Reliability models that rely on equivalent oxide thickness (EOT) based on a small sampling of production wafer kerf structures do not account for the inherent process variability in the deposition of the gate oxide layer across the wafer.